Question

A gas cylinder contains $5\text{ }moles$ of oxygen gas. The weight of the gas in the cylinder is:
A.$~80g$
B.$~120g$
C.$160g$
D.$40g$

Answer 1

In order to solve this question we will first calculate weight of one mole of oxygen gas.
Then we will multiply it by $5$ to get the weight of $5\text{ }moles$

Complete step by step answer:
The molecular mass of oxygen is $16$. The molecule of oxygen exists in the form of $O2$. It has an atomic number $8$. In the given question, we will be using the unitary method. The unitary method is a simple technique which is used for solving a problem just by first finding the value of a single unit, and then determining the needed value by simply multiplying the single unit value. In conclusion, this method is basically used to find the value of a unit ,and hence the value of a multiple.
So first we calculate the value of one mole of oxygen gas, that is
$16\times 2=32$
We multiplied it by $2$ because the oxygen gas exists in diatomic form. So we take the value of both the oxygen atoms.
Now, in order to calculate the weight of five moles of oxygen gas, we will multiply the value of one mole of oxygen gas with $5$,
$5\times 32=160g$
So we got $160g$ as the weight of $5$ moles of oxygen gas.
If we take a look at the options, we can see the value of weight which we calculated matches the value which is given in the option C.
So the correct option is option C.

Additional information:
An example usage of unitary method for better understanding, if a car runs $44\text{ }km$ on $2\text{ }litres$ of petrol then we can use the unitary method to find out the number of kilometres it will cover on $1\text{ }litre$ of petrol. In other words, it is the method by which we can find out the value of one unit and further we could use it to find the value of multiple units is known as the unitary method.

Note:
Most commonly the oxygen exists in the form of $O_2$ as it is the most stable form . But it can also exist in singlet form called nascent oxygen, the word nascent means newborn, as it can only be prepared by certain reactions, it cannot exist naturally. And a triplet form is called ozone.